Nanocrystalline Y2BaCuO5 was prepared by a wet sonochemical process using Y2O3, CuCl2 and BaCl2 as starting material. The influence of ultrasonic power on the crystallization and synthesized activation energy of Y2BaCuO5 were particularly investigated. Results show that the particle size and synthesized activation energy of Y2BaCuO5 decrease with the increase of ultrasonic power. Upon increasing of ultrasonic power from 100 W to 300 W, the particle size and synthesized activation energy of Y2BaCuO5 decrease from 50 nm to 30 nm and from 65 kJ/mol to 47 kJ/mol, respectively.